The invention relates to the field of analog-to-digital converters, and in particular to an analog-to-digital converter that uses multiple analog-to-digital converters (ADC) to improve dynamic range performance.
Digital signal processing has become a very important technology in many application areas including communications, radar, sonar, and many consumer electronic applications. Many of these applications use high dynamic range used in ADCs to convert analog sensor signals into digital data. However, the dynamic range of standard ADCs has been increasing only marginally with time. Typical improvement over the last few years has been approximately 1 dB per year, or equivalent 1 effective bit every 6 years for a given Nyquist sampling rate. Dynamic range is typically defined as signal to noise and distortion ratio (SINDR). It is the ratio between signal level versus the sum of noise, harmonic spurs, and intermodulations at the output of an ADC.
Further, the dynamic range also depends on sampling rate. For any given ADC device, it is generally know that it is possible to increase the dynamic range approximately 6 dB, if the Nyquist rate is reduced by half.
One should be able to increase the sampling rate without reducing the dynamic range by using multiple ADCs. For example, one can use multiple ADCs in round robin fashion to increase the sampling rate. If N ADCs were used, the sampling rate would be increased N times. However, there are many practical difficulties in implementing this scheme. One difficulty is that a high-dynamic range high-speed sample and hold (S/H) circuitry is needed to make this scheme work, and such sample and hold circuitry is difficult to build. The S/H circuitry needs to work N times faster with this scheme. In addition, variations in gain, offset, and sampling clock delays among multiple ADCs typically reduce the dynamic range gain of such systems.
Accordingly, the invention provides an analog-to-digital converter (ADC) with significantly improved dynamic range performance. The invention uses multiple ADCs with independent dither signals and digital processing to improve the dynamic range performance. This scheme provides superior performance because of relative insensitivity to device and circuitry mismatches and imperfections.
According to one embodiment of the invention, there is provided an analog-to-digital converter. The analog-to-digital converter includes a fanned out module for receiving an input signal and producing a plurality of new signals. A plurality of analog to digital converter modules receive the new signals from the fanned module. Each of the new signals is assigned at least one of the analog to digital converters, such that the digital converter modules produce a plurality of digitized signals from each of their associated new signals. A combiner module receives the plurality of digitized signals. The plurality of digitized signals are combined to form a single digitized signal.
According to another embodiment of the invention, there is provided a method of converting an analog signal into a digital signal. The method includes receiving as input the analog signal, and producing a plurality of independent new signals from the analog signals. Each of the independent new signals is assigned to one of a plurality of analog to digital modules, and performing on each of the independent new signals analog to digital operations, such that a plurality of digitized signals are produced. Equalization operations are performed on each of the digitized signals, so that imperfections are removed from the digitized signals. The digitized signals are combined to form the digital signal.
According to another aspect of the invention, a method for analog-to-digital converting is provided. The method includes receiving an input signal and producing a plurality of new signals. Each of the new signals is assigned at least one of a plurality of analog to digital modules, such that the analog to digital modules produce a plurality of digitized signals from each of their associated new signals. The method further includes receiving the plurality of digitized signals. The plurality of digitized signals are combined to form a single digitized signal.